The present invention relates to a novel polypeptide produced by certain kinds of cancer cells, more particularly to a polypeptide whose N-terminus is EAQ and which is composed of 60 amino acids.
It has been reported that `transformed cells` react with substances produced by themselves and thereby self-propagate [M. B. Spora et al., Nature 313, 745-747 (1985)]. This mechanism is called autocrine and has received much attention in connection with carcinomas and the like in recent years.
Of the cancer cells which are `transformed cells`, human breast cancer cell MCF7, for example, has been shown to secrete transforming growth factors .alpha., .beta. and .gamma. [Dickson et al., Cancer Res. 46, 1707-1713 (1986)], insulin-like growth factor [Haff et al., Cancer Res. 46, 4613-4619 (1986)]and platelet-derived growth factor [Brouzert et al., Pro. Natl. Acad. Sci. U.S.A. 84, 5763-5767 (1987)].
As to mRNA induced with estrogen in human breast cancer cells, its complete nucleotide sequence has been elucidated by Chambon et al., and the presence of a polypeptide (9140 daltons) composed of 84 amino acids has been predicted from this nucleotide sequence. It is further predicted from this amino acid sequence that a polypeptide actually secreted may be one (6450 daltons) composed of 58 amino acids or one (6970 daltons) composed of 63 amino acids [Chambon et al., Nucleic Acids Research 12, No. 6, 2861-2878 (1984), and Chambon et al., DNA 4, 11-21 (1985)]. However, this is nothing more than an assumption, and such secreted polypeptides have not been actually isolated and purified to such a degree that their amino acid sequence can be determined.
Thus there has been a long felt need in this field for the isolation and purification of the polypeptides secreted by the breast cancer cells MCF7 and the like, particularly for the elucidation of any relationship between the